1. Field of the Invention
This invention pertains, in general, to the field of retractable covers or roofs for large structures, such as athletic stadiums. More specifically, the invention relates to an improved roof assembly that is lighter in weight, less bulky and less likely to obstruct the vision of spectators within the stadium than comparable mechanisms heretofore known.
2. Description of the Related Technology
It is common in today""s environment for athletic stadiums to be constructed with retractable roofs, because this type of construction offers spectators the pleasure of being outdoors on nice days, while providing shelter when necessary against extreme temperatures and inclement weather conditions. A retractable roof also makes possible the growth of natural grass within the stadium, which is increasingly felt to be desirable in professional and major collegiate athletics.
A number of factors must be taken into account in the design of a stadium that has a retractable roof. For instance, the forces created by the exertion of natural forces such as wind, rain snow and even earthquakes on such a large structure can be enormous, and the roof, the underlying stadium structure and the transport mechanism that is used to guide and move the roof between its retracted and operational positions must be engineered to withstand the worst possible confluence of such forces. In addition, for reasons that are both aesthetic and practical, it is desirable to make the structural elements of the roof and the transport mechanism to be as unobtrusive and as space-efficient as possible. It is also desirable to make the roof structure and the transport mechanism as lightweight as possible, both to minimize the amount of energy that is necessary to open and close the roof structure and to minimize the need for additional structural reinforcement in the roof structure and in the underlying stadium structure. Most conventional stadium roof designs utilize a plurality of structural trusses, each of which spans a distance between a first location on one side of the stadium and a second location on an opposite side of the stadium. A truss is a simple skeletal structure of individual structural members that, according to static analysis theory, will only be subject to tension and compression forces and not bending forces. The most simple type of truss, known as the Warren truss, includes parallel upper and lower horizontal elements and a plurality of diagonal elements connecting the upper and lower horizontal elements. When a bending stress is applied to the truss, the diagonal elements will assume the stress, either as tension or compression, depending upon the orientation of the diagonal element. A structural truss that must span the type of distance that is typical in a stadium, however, typically requires vertical structural elements as well as diagonal elements to provide additional strength.
For a number of reasons, it is considered undesirable to elevate the roof structure any great distance above the main structural mass of the stadium. Unfortunately, since the seating area of the stadiums extends to the very top of the stadium, in many stadiums the structural trusses of the roof interfere with the view from some seats.
A need exists for an improved stadium roof design that will be lighter in weight, less bulky and less likely to interfere with the view of spectators within the stadium than the conventional stadium roof designs discussed above.
Accordingly it is an object of the invention to provide an improved stadium roof design that will be lighter in weight, less bulky and less likely to interfere with the view of spectators within the stadium than the conventional stadium roof designs discussed above.
In order to achieve the above and other objects of the invention, a roof assembly for a stadium that is constructed according to a first aspect of the invention includes at least one major truss spanning a distance between a first support location and a second support location that is at least 200 feet, the major truss being structurally configured as a tied arch having a curved convex upper portion and a lower portion that is shaped, sized and positioned to assume most gravity induced stress within the major truss as tension; and at least one roof member that is secured to said the truss.
According to a second aspect of the invention, a convertible stadium assembly includes a stadium having an exhibition area, a seating area and a plurality of roof support locations, a first major truss spanning a distance between a first of the roof support locations and a second of the roof support locations that is at least 200 feet, the first major truss being structurally configured as a tied arch; a second major truss spanning a distance between a third of the roof support locations and a fourth of the roof support locations that is also at least 200 feet, the second major truss also being structurally configured as a tied arch, a first guide track mounted to the first major truss, a second guide track mounted to the second major truss, a movable roof member that is mounted for movement along the first guide track at a first location and that is further mounted for movement along the second guide track at a second location, a drive system for moving the movable roof member along the first and second guide tracks; and a control system for controlling the drive system.
A convertible stadium assembly that is constructed according to a third embodiment of the invention includes a stadium having an exhibition area, a seating area and a plurality of roof support locations; a first support structure spanning a distance between a first of the roof support locations and a second of the roof support locations that is at least 200 feet; a second support structure spanning a distance between a third of the roof support locations and a fourth of the roof support locations that is also at least 200 feet; a first guide track mounted to the first support structure, the first guide track being shaped so as to be continuously convexly upwardly curved; a second guide track mounted to the second support structure, the second guide track being shaped so as to be continuously convexly upwardly curved; a movable roof member that is mounted for movement along the first guide track at a first location and that is further mounted for movement along the second guide track at a second location; a drive system for moving the movable roof member along the first and second guide tracks; and a control system for controlling the drive system.
These and various other advantages and features of novelty that characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to the accompanying descriptive matter, in which there is illustrated and described a preferred embodiment of the invention.